dependencymanager/org.apache.felix.dependencymanager.annotation/src/org/apache/felix/dm/annotation/api/AdapterService.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.felix.dm.annotation.api;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Annotates an Adapater service component. Adapters, like {@link AspectService}, are used to "extend" 
 * existing services, and can publish different services based on the existing one. 
 * An example would be implementing a management interface for an existing service, etc .... 
 * <p>When you annotate an adapter class with the <code>@AdapterService</code> annotation, it will be applied 
 * to any service that matches the implemented interface and filter. The adapter will be registered 
 * with the specified interface and existing properties from the original service plus any extra 
 * properties you supply here. If you declare the original service as a member it will be injected.
 * 
 * <p> For "add", "change", "remove" callbacks, the following method signatures are supported:
 * 
 * <pre>{@code
 * (Component comp, ServiceReference ref, Service service)
 * (Component comp, ServiceReference ref, Object service)
 * (Component comp, ServiceReference ref)
 * (Component comp, Service service)
 * (Component comp, Object service)
 * (Component comp)
 * (Component comp, Map properties, Service service)
 * (ServiceReference ref, Service service)
 * (ServiceReference ref, Object service)
 * (ServiceReference ref)
 * (Service service)
 * (Service service, Map propeerties)
 * (Map properties, Service, service)
 * (Service service, Dictionary properties)
 * (Dictionary properties, Service service)
 * (Object service)
 * }</pre>
 * 
 * <p> For "swap" callbacks, the following method signatures are supported:
 * 
 * <pre>{@code
 * (Service old, Service replace)
 * (Object old, Object replace)
 * (ServiceReference old, Service old, ServiceReference replace, Service replace)
 * (ServiceReference old, Object old, ServiceReference replace, Object replace)
 * (Component comp, Service old, Service replace)
 * (Component comp, Object old, Object replace)
 * (Component comp, ServiceReference old, Service old, ServiceReference replace, Service replace)
 * (Component comp, ServiceReference old, Object old, ServiceReference replace, Object replace)
 * (ServiceReference old, ServiceReference replace)
 * (Component comp, ServiceReference old, ServiceReference replace)
 * }</pre>
 * 
 * <h3>Usage Examples</h3>
 * 
 * <p> Here, the AdapterService is registered into the OSGI registry each time an AdapteeService
 * is found from the registry. The AdapterImpl class adapts the AdapteeService to the AdapterService.
 * The AdapterService will also have the following service property: p1=v1, p2=v2 :
 * <blockquote>
 * <pre>
 * 
 * interface AdapteeService {
 *     void method1();
 *     void method2();
 * }
 * 
 * &#64;Component
 * &#64;Property(name="p1", value="v1")
 * class Adaptee implements AdapteeService {
 *     ...
 * } 
 * 
 * interface AdapterService {
 *     void doWork();
 * }
 * 
 * &#64;AdapterService(adapteeService = AdapteeService.class)
 * &#64;Property(name="p2", value="v2")
 * class AdapterImpl implements AdapterService {
 *     // The service we are adapting (injected by reflection)
 *     volatile AdapteeService adaptee;
 *   
 *     public void doWork() {
 *        adaptee.method1();
 *        adaptee.method2();
 *     }
 * }
 * </pre>
 * </blockquote>
 * 
 * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a>
 */
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.TYPE)
public @interface AdapterService
{
    /**
     * Sets the adapter service interface(s). By default, the directly implemented interface(s) is (are) used.
     * @return the adapter service interface(s)
     * @deprecated you can apply {@link Property} annotation directly on the component class.
     */
    Class<?>[] provides() default {};

    /**
     * Sets some additional properties to use with the adapter service registration. By default, 
     * the adapter will inherit all adaptee service properties.
     * @return some additional properties
     */
    Property[] properties() default {};

    /**
     * Sets the adaptee service interface this adapter is applying to.
     * @return the adaptee service interface this adapter is applying to.
     */
    Class<?> adapteeService();
    
    /**
     * Sets the filter condition to use with the adapted service interface.
     * @return the adaptee filter
     */
    String adapteeFilter() default "";
    
    /**
     * Sets the static method used to create the adapter service implementation instance.
     * By default, the default constructor of the annotated class is used.
     * @return the factory method
     */
    String factoryMethod() default "";
    
    /**
     * Sets the field name where to inject the original service. By default, the original service is injected
     * in any attributes of the adapter implementation that are of the same type as the adaptee interface.
     * @return the field used to inject the original service
     */
    String field() default "";
    
    /**
     * The callback method to be invoked when the original service is available. This attribute can't be mixed with
     * the field attribute.
     * @return the add callback
     */
    String added() default "";

    /**
     * The callback method to be invoked when the original service properties have changed. When this attribute is used, 
     * then the added attribute must also be used.
     * @return the changed callback
     */
    String changed() default "";

    /**
     * name of the callback method to invoke on swap.
     * @return the swap callback
     */
    String swap() default "";

    /**
     * The callback method to invoke when the service is lost. When this attribute is used, then the added attribute 
     * must also be used.
     * @return the remove callback
     */
    String removed() default "";
    
    /**
     * Specifies if adaptee service properties should be propagated to the adapter service.
     * The component provided service properties take precedence over the propagated adaptee service properties, meaning
     * that a give component service property overrides the same property present in the propagated adaptee service properties.
     * @return the service propagation flag
     */
    boolean propagate() default true;
    
	/**
	 * The service scope for the service of this Component.
	 * 
	 * <p>
	 * If not specified, the {@link ServiceScope#SINGLETON singleton} service
	 * scope is used. 
	 */
	ServiceScope scope() default ServiceScope.SINGLETON;
}